Airplane



April 16, 1940- o. c. kbPPEN 2,196,994

AIRPLANE Filed Feb. 23, 19:59 2 Sheets-Sheet 1 TUNNELTEST EFFECTIVE REYNOLDS NO. 2 so, 0 o O INVENTOR BY I ATTORNEY 1.1.1 5FTWIND Patented Apr. 16,1940 I I 2 19 994 f UNITED- STATES PATENT orncsz Otto C. Koppen, Waban, Mass, assiznor to Edward J. Frost, Auburndale, Mass" as trustee Application February 2a, 1939, Serial No. 357,863

' Claims. (CL 244 This invention relates to airplanes and has for gerous degree, particularly at low air speeds and its object to provide a directionally stable, twoat high angles of attack. This has remained true' control airplane constructed and arranged to be despite efforts to eliminate or such disflown with ailerons and elevator only, that is, advantages-by various means such as angularly 5 a practicable rudderless airplane. Such airplane disposed vertical flns (with resultant increase in' is capable of satisfying the present and growing drag), trimming means (which are really in the demand for a simplified, more easily controlled nature of a rudder), and even a rudder or rudand safer airplane which obviates the necessity ders tied in with and actuated by the aileron of so much training and skill, as at present recontrol stick or wheel, thus 'really making a 9 quired, before one is able properly and safely to three-control airplane. Such additional and m fly an airplane. cumbersome means and devices have adversely In the drawings Figure 1 is a graph showing affected both the control and performance, as yawing moment coeflicients plotted against angles well as the safety of such two-control airplanes of yaw; Figure 2'is a plan view of an aircraft as have yet been known. 1

according to a preferred embodiment of my in- I have discovered how to construct a two-convention; Figure 3 is a side elevation thereof and trol or rudderless airplane which can be flown Figure 4 is a front elevation of'said aircraft. with adequate and positive control by ailerons Practically all present day airplanes are of the and elevator only, and which wholly avoids all of: three-control type with ailerons and elevator the above mentioned defects and disadvantages I operated by the hands and with a rudder operated of that type, and possesses, moreover, many adby the feet.. It requires a considerable amount vantages over known airplanes, whether of the of training, skill, and frequent practice in order three-control or of the two-control type. This that one may properly and safely coordinate the invention provides a successful, simple two-conmovements of the hands in the .operation of the trol airplane which in flight has proved to be 85 ailerons and of the feet. in the operation of the directionally stable to an exceptional" degree, in rudder, as required in all such present day threerough as well as smooth air; which byaileron control airplanes. This coordination requires movement only can be smoothly turned, grad.- operation of both the ailerons and: the rudder to ually or sharply as required,even by inexpecolmteract the disturbances to stable flight and to rienced pilots; which does not wallow or swerve turn and maneuver the airplane. These disfrom side to side in either straight or turning turbances are commonly due to rough air and to flight; which has neither material hesitation nor yaw and dr f most yp of ailerons When aileron yaw either in initiating or recovering p es e m k a u n nd in s shte s from atum; and which compensates for damp out after a turn: Coordination of the rudder and V of w i a m n of which desirable the ailerons is necess ry also t minim fcharacteristics are present whether the airplane ing, (particularly in airplanes having a low ratio be in climbing, cruising, or gliding flight. or

of directional to lateral stability), -The chief whether it be taking off or n functions of an airplane rudder are to overcome In, the design of airplans the factor of aileron yaw; to counteract the yawing moment I 40. due to rolling velocity; to overcome the damping mg moment must be and has been taken into t. As is well known, when an airplane of yaw in a steady turn, and to counteract the effects of the rotation of the propeller slip-stream.- is tamed to an angle of yaw to Its duectmn In an these circumstanm they-rudder must be oLflight, it. presents surfaces at such angle of moved to the proper extent, at the proper time, yaw to the Such surfaces have an I5 and at the proper rate, in varying degree as eifective area aand a center of pressure which a. mam-led by the particular fl t, conditions is located in the airplane at a distance 1 behind fling a vertical a ds through the centerpo'f gravity. Because-of these conditions which require a The force, fitting-at nt r of pressure, rerudder, and in spite of the demand for simplified (mired to balance'the force. exerted by the air 0 airplanes-only a very few two-control or rudflow and tending to restore the longitudinalaans derless airplanes have been built and flown. of'the airpiane to its direction of,flight m ay be But in such two-control airplanes many, if not called 10. The yawing moment is theproduct all, of the above mentioned conditions for which of those three factors, i. e. yawing moment the rudder is used in three-control airplanes are equals axlxw. Of these factors, a and l are ll still presentto an objectionable and even danconstants for a given airplane, but w varies "-3 vention, with the slope of the yawing moment with the angle of yaw through which the airplane has turned.

The yawing momentcoificient Cu, as is well known in the art, is obtained by-the following formula:

yawing' moment qXSXb q=dynamic pressure=% d=the density of the air v=the velocity of the air S=wing area b=wing span On (yawing moment coeiilcient) may be plotted on the axis of Y in the usual system of ordinates against 1/1 (the angle of yaw) on the axis of X. This plot results in a line or curve passing through the origine and having a slope, i. e. making an angle with the axis of X. This line is known in the art as the yawing moment curve. In the U. S. National Advisory Committee for Aeronautics sign convention employed in this country and used herein, a negative sign of the slope of the yawing moment curve indicates directional stability.

I have discovered that a rudderless airplanetunnel tests of ascale model of the rudderless airplane of this invention.

That the principles of my invention involve a radical departure from present practice is illustrated by comparing the slope of the yawing moment curve, which is characteristic of my incurv of an airplane of equal wing-loading. for example, of a three-control airplane having a wing loading of 10 lbs. per square foot, representing an average of 5-15 lbs. wing loading of present-day normal general-purpose airplanes in common use. The invention, however, may be employed in airplanes having wing loadings in excess of 15 lbs. per square foot.

In Figure 1 line 0A represents the conventional 'practice and requirements in three-control airplanes based on the accepted authority of Engineering Aerodynamics, by Walter S. Diehl, 1936 rev. ed., p. 206. This practice has also been followed in the design of two-control airplanes. The line CA has a slope from the horizontal axis of x of .0005 Cu per degree of angle oi yaw.

The slope of the line OB represents (in terms of Cu per degree of angle of yaw) what I have found by actual flight to be the practicable minimum in a rudderless airplane embodying my invention, i. e. .0020 per degree. This, in the above comparison, is four times the value of Diehls criterion of directional stability.

The slope of the line OC represents what I have, found by actual flight, to give optimum results, i. e. .0028 per degree. This, in the above comparison, is 5.6 times the value of Diehls criterion of directional stability. Expressed trigonometrically, the line OB, representing my minimum, has a negative slope or tangent which is four times the tangent of the Diehl line 0A, and my optimum line 00 has a negative slope of experience to date.

aromas or-tangent which is 5.6 times the tangent of the Diehl line.

Substantial benefits can be obtained in rudder-- less airplanes embodying-the principles of my invention having negative slopes of yawing moment curves somewhat less than .0028 per degree and down to the minimum of -'-.0020 per degree, but at some sacrifice of directional stability-and control, turning characteristics, and responsiveness, particularly at less than cruising speed. It is preferred to have an airplane which embodies a yawing moment curve having a slope of the order of .002'7 to -.0030 per degree, which is in the range of the optimum in view Full benefits of the invention, however, from the standpoints of'stability, turning, and control, can be obtained by an airplane embodying a yawing moment curve having a slope in excess of the said optimum, but with some limitations on account ofconsiderations of weight, dimensions, structural strength of fuselage required, expense,andfappearance.

high-wing bracedmonoplane with tricycle landing gear, three views are shown in the drawings. Though the invention is here shown only in connection with a small 7 single propeller airplane, it is applicable'to both single and multi-propeller airplanes of various types and sizes. Though the invention has been described only in connection with airplanes having rearwardly extending means for supporting tail portions (such as a fuselage or booms), the principles of the invention are also applicable to tailless airplanes in which the wings are swept-back sufliciently so that the necessary vertical fin surfaces may be aiiixed at or near the ends of the wingsand rearwardly of the center of gravity.

Referring to the drawings, in which like numerals represent like parts, the wing 2 of the conventional airfoil section having ailerons 4 and flaps 6 is afiixed to fuselage 8 and braced therefrom by braces 9. To the fuselage 8 are suitably afflxed main landing wheels l0 and nose wheel l2, though present-day conventional landing gear with suitable brakes will answer. Th'e'fuselage 8 carries at the rear end thereof a stabilizer I il having hingedly aifixed thereto elevator l6.

The ailerons andelevator may be controlled by either a stick or Deperdussin wheel (not shown). The foregoing is common practice. The

' airplane has no rudder, and aflixed to the stabilizer is a pair of vertical fins l8 substantially par allel to the longitudinal axis of the fuselage. These fins are sufficiently spaced apart,-as shown,

- so as to be substantially free from the turning 'of my invention, the optimum aggregate area of v the vertical fins in the airplane herein shown is of the order of 20%-22% of the wing area, thus providing a yawing moment curve with aslope of substantially .0028 for each degree of angle of yaw, the line 00 of Fig. 1. The practicable minimum of the ratio of aggregate fin area to wing area in this airplane is about 14% or 15%, which corresponds to the line OB of Fig. 1. I r I There may be a single fin or a plurality of fins and placed as to avoid the turning and rolling effect of propeller slip-stream rotation. If there are several fins they must be spaced sufiiciently far apart to avoid interference.

The rudderless airplane of this invention, as a practical matter and in all normal conditions of flight, maintains a substantially zero angle of yaw. Thus, it maintainsstraight fiight or turning flight, as the case maybe, when the ailerons are in neutral, but also properly turns or straight-* ens from a turn, as the case may be, when the ailerons are displaced from neutral.

Having described my invention and typical preferred embodiment thereof, I claim:

1. In a rudderless airplane, a supporting wing, ailerons on the wing, a fuselage having nose, body and tail portions, a stabilizer andelevator mounted on the rear end of the fuselage, and laterally spaced fixed vertical fins, the length of said tail portion and the aggregate area of said vertical fins being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope in excess of minus .0020 per degree of angle of yaw.

2. l'n a rudderless airplane, a supporting wing,

ailerons on the wing, a fuselage having nose,

body and tail portionaa' stabilizer and elevator mounted on the rear end of the fuselage, and laterally spaced fixed vertical fins, the length of said tail portion and the aggregate area of said vertical fins being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope of the order of minus .002'i.0030 per degree of angleof yaw.

3. In arudderless airplane, a body, a supporting wing, ailerons onthe wing, tail group supporting means, a tail group including a stabilizer, elevator, and laterally spaced fixed vertical fins, the length of said tail group supporting means and the aggregate area of said vertical fins being such as with-the aforesaid related elements of the airplane to provide a stable yawing momentcurve having a slope in excess of minus .0020 per degree of angle 01' yaw. e

'- 4. In a rudderless airplane, a body, a supporting wing, ailerons on the wing, tail group supporting means, a tail group including a stabilizer,

elevator, and laterally spaced fixed vertical fins,

the length of said tail group supporting means and the area ofsaid vertical fins being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope of the order of minus .002'7-.0030' per degree of angle of yaw.

5. In a rudderless airplane, a supporting wing, ailerons on the wing, at fuselage having nose, body and tail portions. a stabilizer and elevator, and at least one fixed vertical fin, the length of said tail portion and the aggregate vertical fin area being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope'inexcess of minus .0020 per degree of angle of yaw.

6; In a rudderless airplane, a supporting wing,

ailerons on thawing, a fuselage having nose,

body and tail portions, a stabilizer and elevator, and at least one fixed vertical fin, the length'of said tail portion and the aggregate vertical fin area being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope of the order of minus .0027-.0030 per degree of angle of yaw.

7. In a rudderless airplane, a body, a supporting wing, ailerons on the wing, tail group sup porting means, a tail group including a stabilizer, elevator, and at least one fixed vertical fin, the length of said tail group supporting means and the aggregate vertical fin area being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope in excess of minus .0020 per degreev of angle of yaw.

8. In a rudderless airplane, a body,- a supporting wing, ailerons on the wing, tail group supporting means, a tail group including a stabilizer,

elevator, and at least one fixed vertical fin, the length of said tail group supporting'means and the aggregate vertical'fin area being such as with the aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope of the order of minus .0027.0030 per degree of angle of yaw.

' 9. In a rudderless airplane, a body, a supporting wing, ailerons on the wing, a plurality of fixed vertical fins positioned and held rearwardly of the center of gravity of the airplane, the aggregate vertical fin area' and the distance thereof aforesaid related elements of the airplane to provide a stable yawing moment curve having a slope of the order of minus .0027-.0030 per degree of angle of'yaw.

10. me rudderless airplane, a body, a supporting wing, ailerons on the wing, a plurality of 'flxed vertical fins positioned and held rearwardly in excess of minus .0020 per degree of angle of yaw.

O'I'IO C. KOPPEN'.

from the center of gravity being such aswith'the 

